Abstract
Intense transport of bed load is associated with highconcentrated sediment-laden flow over a plane mobile bed at high bed shear. Typically, the flow exhibits a layered internal structure in which a vast majority of sediment grains is transported through a collisional layer above the bed. Our investigation focuses on steady uniform open-channel flow with a developed collisional transport layer and combines modelling and experiment to relate integral quantities, as the discharge of solids, discharge of mixture, and flow depth with the longitudinal slope of the bed and the internal structure of the flow above the bed. In the paper, flow with the internal structure described by linear vertical distributions of granular velocity and concentration across the collisional layer is analyzed by a model based on the classical kinetic theory of granular flows. The model predicts the total discharge, the discharge of sediment, and the flow depth for given (experimentally determined) bed slope and thickness of collisional layer. The model also predicts whether the intefacial dense layer develops between the bed and the collisional layer and how thick it is. Model predictions are compared with results of intense bed-load experiment carried out for lightweight sediment in our laboratory tilting flume.
Highlights
For intense bed load transport, collisional interactions of transported sediment grains are typical and they significantly affect behaviour of flow carrying the sediment above a plane mobile bed at high bed shear
The dense limit condition (e.g. [3]) is not assumed at the bottom of the collisional transport layer because our experiments indicated that for studied flow conditions the local concentration at the bottom of the collisional layer varied considerable with the bed shear stress
In the presented kinetic-theory based model, constitutive relations of the classical kinetic theory allow to predict the discharges of sediment and mixture, the flow depth and the thickness of the sliding dense layer in flow carrying intense bed load at conditions observed in a tilting-flume experiment
Summary
For intense bed load transport, collisional interactions of transported sediment grains are typical and they significantly affect behaviour of flow carrying the sediment above a plane mobile bed at high bed shear (the upper-stage bed regime). The flow exhibits a layered structure in which a vast majority of grains is transported through a collisional transport layer. The collisional layer dominates the internal structure of the flow. Appropriate modelling of friction and transport in the layered structure of the flow is crucial for prediction ability of a bed-load transport model. Kinetic-theory based models for contact-load transport in open-channel flow enable a prediction of relevant flow quantities in a layered pattern of the flow. We aim on formulating a simple kinetic-theory-based model to evaluate flow conditions observed in our intense-bed-load experiment in a laboratory tilting flume
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